Situation
A distribution warehouse expanded sortation capacity by adding zones, but each zone PLC operated semi-independently. Jams cascaded; forklift drivers coordinated restarts by radio, wasting minutes per incident.
Problems encountered
- No shared line speed reference—zones accelerated into full buffers.
- Photoeye placement missed cartons on certain merge angles.
- E-stop wiring caused entire loop outages for local jams.
Engineering response
We implemented coordinated speed trim based on downstream occupancy, with explicit jam states per zone. Merge logic gained redundant detection and timed confirmation before declaring clear. E-stop zoning was revised with electrical contractor so local jams did not require whole-loop resets.
Outcomes
Jam recovery on monitored shifts was faster once zones held and released automatically. Throughput was steadier during peak promotional periods. Radio traffic reduced as operators relied on the hold/resume logic.